The physical and mechanical properties of foams make them useful for a wide variety of applications, including upholstery and bedding. However, many foams, for example polyurethane, are inherently flammable and lead to melting and spread of burning debris. In the case of many "conventional" foams such characteristics lead to the sustaining of combustion by progressive smoldering even after the actual flames have extinguished.
It is considered that cellular materials manufactured from flammable polymers are more flammable than the solid materials because the insulating effect of their cellular nature allows a rapid build-up of heat at the heating surface with a consequence high rate of pyrolysis. In solid materials this heat build-up is at a lower rate because of the higher conductivity of the solid material. Although rigid foams have similar thermal conductivity behavior to flexible foams, the high cross-linked nature of their chemical structure makes them less flammable as polymers and also inherently more inclined to form a protective char rather than to form the flaming molten polymer droplets which occur with flexible foams. While both solid and rigid cellular materials burn less easily than flexible foams and are easier to extinguish, they tend to smolder and emit toxic fumes.
The use of polyurethane foams in airplanes is a particular concern. Fires in airplanes are difficult to extinguish when they start since adequate firefighting equipment is not readily available because of weight and size limitations in storage on the aircraft and the inability to maneuver around the passengers. It is therefore desirable to provide a polyurethane foam for use as seat cushions which is fire retardant, does not smolder and is self-extinguishing.
Various methods are known to reduce the flammability of polymer foams. Commonly, additives such as aluminum trihydride or phosphous-containing compounds are incorporated into the foam for this purpose. Alternatively, halogenated polyols, especially brominated polyols such as dibromoneopentyl glycol, are used to increase the flame resistance in the foam. None of these additives have proved entirely satisfactory.
It is known that the incorporation of trimerized polyisocyanates (i.e. isocyanaurates) into a foam improves its burn characteristics. For example, trimerized toluenediisocyanate has been used to prepare flexible foams. Although these foams do exhibit good foam characteristics, they also have poor physical properties, particularly poor compression sets and partial cell collapse. In addition, trimerized toluene diisocyanate tends to precipitate from the isocyanate solution in which its is dissolved, causing storage problems and a lack of uniformity in foams prepared therewith.
Each of U.S. Pat. Nos. 4,554,293; 4,528,300 and 4,640,933 to Park, which are herein incorporated by reference disclose polyolefin resin foams which can be used in the present invention.
U.S. Pat. No. 4,699,931 to Fuzesi, et al which is herein incorporated by reference, discloses polyol-free isocyanurate foams which can be used in the present invention.
U.S. Pat. Nos. 4,489,913; 4,552,903; 4,574,137; 4,581,418 and 4,596,665, which are all herein incorporated by reference, disclose the different types of polyurethane foams which may be utilized in the invention and whose flame retarding characteristics can be improved by the method hereinafter described.
U.S. Pat. Nos. 3,770,668 and 3,960,792 which are herein incorporated by reference, disclose typical polystyrene foams which can be utilized in the present invention.
U.S. Pat. No. 4,699,943 to Bertrand, which is herein incorporated by reference, discloses self-extinguishing polystyrene compositions with improved thermal properties. The polystyrene foams are blended with a fire retarding agent consisting of tribromopentaerythritol. There are also disclosed polystyrene compositions whose self-extinguishing characteristics can be further improved by the present invention.
European Patent Application No. 0199567 of McCullough, et al, which corresponds to U.S. patent application Ser. No. 856,305, and is herein incorporated by reference, discloses non-linear carbonaceous fibers which are used to provide the improvements in accordance with the present invention.
The carbonaceous fibers of the invention according to the test method of ASTM D 2863-77 have a LOI value greater than 40. The test mehtod is also known as "oxygen index" or "limited oxygen index" (LOI). With this procedure the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is determined at which a vertically mounted specimen is ignited at its upper end just continues to burn. The size of the specimen is 0.65.times.0.3 cm with a length from 7 to 15 cm. The LOI value is calculated according to the equation: ##EQU1##
The term "stabilized" herein applies to fibers or tows which have been oxidized at a specific temperature, typically less than about 250.degree. C. for PAN fibers, provided it is understood that in some instances the filament and/or fibers are oxidized by chemical oxidants at lower temperatures.
The term "Reversible Deflection" as used herein applies to a helical or sinusoidal compression spring. Particular reference is made to the publication "Mechanical Design - Theory and Practice", MacMillan Publ. Co., 1975, pp 719 to 748; particularly Section 14-2, pages 721-24.